Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$134.47	13.674%	$152.8574	$152.86	$152.85	$152.90
Purchase #2	$148.89	12.591%	$167.6367	$167.64	$167.65	$167.60
Purchase #3	$165.40	13.740%	$188.126	$188.13	$188.15	$188.10
Purchase #4	$87.50	3.462%	$90.5293	$90.53	$90.55	$90.50
Purchase #5	$7.96	7.342%	$8.5444	$8.54	$8.55	$8.50
Purchase #6	$48.60	6.375%	$51.6983	$51.70	$51.70	$51.70
Purchase #7	$125.67	11.676%	$140.3432	$140.34	$140.35	$140.30
7 purchase totals =	$718.49		$799.7353	$799.74	$799.80	$799.60